Cook noodles to desired doneness as directed on package. Drain.
Meanwhile, heat oven to 350°F. Spray 2-quart casserole with nonstick cooking spray. In large skillet, combine ground beef, onion and bell pepper; cook over medium-high heat until beef is thoroughly cooked and vegetables are tender. Drain.
Add sandwich sauce, soup and mushrooms; mix well. Heat until bubbly. Gently stir in cooked noodles. Pour mixture into sprayed casserole. Sprinkle with cheese.
Bake at 350°F. for 20 to 25 minutes or until casserole is thoroughly heated and cheese is melted.